ndanger / pycomparable

Add rich comparison special methods (__ne__, __gt__, etc.) to a class

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ce9b6764 » ndanger 2008-10-03 Renamed to match lower-case... 1
2 DISCLAIMER:
3
4 Although this works (it really adds the rich comparison operators), it's for
5 fun/learning purposes only. If you really need all the comparisons, you're
6 probably better off writing __cmp__. I think Python3000 might automatically
7 create __ne__ based on __eq__. The one real world use might be to easily
8 add all rich comparison methods to a subclass where the parent class
9 implements a subset of the operator. But how often does that happen? Just
10 use it for fun.
11
12
13 Try to add rich comparison methods (__eq__, __ne__, etc.) to an existing class.
14 It exports three names:
15
16 * comparable - class decorator
17 * ComparableMetaclass - Metaclass to automatically call comparable
18 * ComparableMixin - Mixin to automatically call comparable
19
20 comparable works as a class decorator. It takes a class as an argument and
21 returns a decorated class. comparable attempts to add the rich comparison
22 special methods if they are not defined. If __eq__ is not defined, it will
23 try to define it as being not != or not (< or >), etc. It then sets != as
24 the inversion of ==. Finally it sets whatever inequalities are possible
25 (e.g. < === <= and not ==).
26
27 comparable will not overwrite existing methods.
28
29 comparable won't add methods if there is not enough information. For
30 example, if only __eq__ and __ne__ are defined, it will not attempt to add
31 any inequalities. It also won't raise any errors, so be warned.
32
33 ComparableMetaclass and ComparableMixin are additional ways to create a
34 comparable class. Both are simply wrappers for the main comparable
35 function.
36
37 Inspired by this discussion turned rant on comp.lang.python
38 (http://groups.google.com/group/comp.lang.python/browse_thread/thread/a5fa8ff0ffadd6ee/1aa3b5d25eae91d5)
39 Loosely based on Ruby's comparable module
40 (http://www.ruby-doc.org/core/classes/Comparable.html) though I believe the
41 implementation is different.